when people say people can be punished in This incarnation for a previous incarnation (like for instance how Job was) for something they did wrong in the past life, even if someone was theoretically perfect in this life, is this ONLY true for when someone in their past life died without doing teshuva OR is it true also for if someone in a past life did teshuva before they died and then still had to like ’repay their sins’ even though they did teshuva? thanks!

As soon as one does teshuva, his sins are totally erased, and often even actually turn into merits! One is not punished for anything after doing total and sincere teshuva, which includes: recognizing and leaving the sin, regret, expressly wording the regret (viduy), accepting in the future not to repeat the sin, and when necessary, asking forgiveness from the other person/people we harmed.